Conventional potentiometers of the said type are comprised of an electrically insulating body forming a cylindrical cup, inside which is housed the resistive plate which adopts the shape of an open circular ring, which plate is secured at its ends to the said cylindrical cup by means of rivets which simultaneously constitute the means for electrically connecting the said resistive plate to the corresponding connecting terminals. The said cup is closed by the complementary collector of the said resistive plate which, in turn, extends radially into the corresponding connecting terminal. A circular ring shaped cursor, which adapts itself to the inner face of the collector, is hinged to an axis of rotation, it is provided with an inclined arem and ends in a projection by means of which it contacts any point of the resistive plate, when the said axis is made to rotate. The said axis is provided at least one of its ends with means enabling any appropriate tool, such as for example a screwdriver, to operate it.
The problems derived from this structure are multiple and varied.
Its cylindrical configuration impedes handling thereof, specifically insofar as its correct positioning with repect to the printed circuit wafer in which it ought to be mounted, when the said assembly takes place automatically.
The angle of rotation of the cursor, which could theroetically be brought markedly closer to the complete turn, is reduced to a value close to 235.degree..
The collector offers a rather small thermal dissipational surface, which negatively affects operation of the potentiometer, and distortions may even be produced therein.
The roughnesses produced in the collector from the cutting operation to obtain the central hole, cause an irregular turning torque.
The plastic flanging for securing the collector to the caisng offers a poor axial thrust resistance on the rotor or cursor.
The control of the turning torque of the rotor and the cursor on the resistive plate is difficult and irregular.
The part of the terminals which are coupled to the printed circuit, is short, obstructing insertion when the terminals have a greater thickness, as also, obviously, the subsequent welding thereof. Supplementarily, and since they are closer to the heating zones, the plastic parts of the component experience deformations during the welding process, which may alter the continuity of the electrical contacts.
With the present clamping system for securing the resistive plate to a surface difficult to control, since this relates to another pre-bent mechanical staple with the logical material recoveries, losses in contact are produced between the terminal and the resistive plate, in the event of a lack of pressure when bending the leg surrounding the resistive plate, whilst in the event of an overpressure, breakage of the said plate may be produced.
The system for clamping the terminals of the casing and the resistive plate causes, at the time of welding thereof to the circuit, when welding takes place manually, by heat radiation and specially due to the fact that the thermal level during manual heating is difficult to control, the plastic materials to become soft, therefore producing intermittent losses in the electric continuity.